Various products can be produced by reacting one or more reactants in the presence of a catalyst. In some reactions, the catalyst can be a different physical state than the one or more reactants. For example, two liquid reactants can be reacted in the presence of a solid catalyst. As an example of a particular reaction using reactants and catalysts having different physical states, an oxirane can be produced by reacting a liquid olefin and a liquid peroxide compound in the presence of a solid catalyst, where such a reaction may also be referred to as an “epoxidation reaction.” Once the reaction is complete, various components of the mixture can be separated to obtain the product (e.g., the oxirane).